A computerized task operated by a single switch was designed to meet the need for a therapy teaching cause and effect to severely and multiply disabled children. Research concentrated on developing adequate analysis techniques for capturing a child’s exploratory interaction with a computer. Initial exploration of the contingencies of the task and development of a performance strategy was investigated with two samples of normal children using different versions of the task. The value of considering the dynamics and competency of performance was established with a case study of a therapy programme with four severely physically disabled but mentally intact children. Robust estimation of performance components and a computerized expert system for data analysis and strategy classification were major analytic innovations.